She was fiery and formidable on screen, but off screen, and in the arms of her lover Marlon Brando, Oscar-winning actress Rita Moreno, best known for her role as Anita in “West Side Story,” was reduced to a withering, suicidal mess.

Her obsessive love for the Method actor “almost proved fatal.” During their eight-year affair, she endured chronic philandering, emotional abuse, a botched abortion — and that’s only the beginning.

“I remember how he spoke to me, how he played the drums, how he made love . . . and how I almost died from loving him,” Moreno, now 81, writes in her new memoir, “Rita Moreno.”

Although Moreno’s life story is fascinating on its own — she’s one of the only people, not to mention the first Hispanic, to receive an Emmy, Grammy, Oscar and Tony — a sizable chunk of the book, about one-third, is devoted to her torrid love affair with Brando.

“We were locked in the ultimate folie à deux, a crazy love that lasted for years, until one day I quite literally was forced out of a coma and had to choose life over him,” she writes.

Ruby Dolores Alverio arrived in The Bronx from Puerto Rico as a 5-year-old. She started taking dance lessons a year later and by 16 was discovered by a talent scout, who recommended her to famed producer Louis B. Mayer.

Mayer took one look at the teen — who had painted herself up to look like Elizabeth Taylor — and in a matter of seconds said, “Sign her!”

The second order of business was getting a Hollywood-friendly name. She was calling herself Rosita Moreno, using her stepfather’s last name, when she met with powerful casting agent Bill Grady, who tried some options out. “Ruby Fontino? Marcy Miranda?” The names got progressively worse. “Orchid Montenegro!”

Then he stopped himself. “I got it! How about Rita, after Rita Hayworth?”

Her voluptuous beauty caught the eye of many older men, including one “very handsome redheaded gentleman” at a hotel opening who was sitting next to a regal companion.

“His hairline moved back an inch, as when a predatory animal spots his prey and paralyzes it with ‘that look.’ It was obviously lust at first sight, and I remember thinking, ‘Whooo, this guy don’t waste no time!’ ” she writes. “I have no doubt that this man would have sent someone over to my table to escort me upstairs.

Weeks later, she sees her admirer in Life magazine — the young senator from Massachusetts, John F. Kennedy, with his wife, Jackie.

Then, in 1954, in a makeup room on the set of Brando’s “Désirée,” in which he played Napoleon, a 22-year-old Moreno met the man who would rock her world.

“Just meeting him that first day sent my body temperature skyrocketing as though I had been dropped into a very hot bath, and I went into a full-body blush,” she writes of meeting the 30-year-old icon-to-be. “It was the sort of rush that inspires poetry and songs.”

The sex was earth-shattering.

“To say that he was a great lover — sensual, generous, delightfully inventive — would be gravely understating what he did not only to my body, but for my soul. Every aspect of being with Marlon was thrilling, because he was more engaged in the world than anyone else I’d ever known,” she writes.

But it wasn’t all roses. He seemed to have a darkness, a deep well of need, stemming from his childhood with an alcoholic mother.

Possibly as an outgrowth of this, he had “insatiable sexual needs,” which he unabashedly pursued with droves of other women.

“He broke my heart and came close to crushing my very spirit with his physical infidelities and, worse, with his emotional betrayals,” she writes.

During their relationship, he married twice and fathered children with his wives.

But “I couldn’t stay away. In fact, I was becoming addicted to the challenge of winning him over and over again,” Moreno says.

Often the way to win him over was to date other men. Moreno took up with a disappointing Dennis Hopper, then with “a human missile . . . Elvis.”

“I knew no one could possibly make Marlon Brando more jealous,” she writes.

During a particularly bad rough patch with Brando — she had discovered a woman’s nightgown in Brando’s closet — Moreno read a gossip item about Presley wanting to meet her. To spite Brando, she agreed. (Ironically, Presley was “obsessed” with Brando and even styled himself after Brando’s “The Wild One” character.)

But the King was no match for Brando.

“My dates . . . nearly always concluded in a tender tussle on my living-room floor, with Elvis’ pelvis in that famous gyration straining against his taut trousers. I could feel him thrust against my clothed body, and expecting the next move . . . but it never came,” she writes.

“Grinding” was all Elvis wanted to do. According to other girls, it seemed to be his modus operandi. He liked to cuddle with his teenage fans or watch girl-on-girl action. But no sex.

“Maybe Elvis was inhibited by inbred religious prohibitions or an Oedipal complex, or maybe he simply preferred the thrill of a denied release. Whatever put the brakes on the famous pelvis, it ground to a halt at a certain point and that was it,” she writes.

One day, while watching him devour a peanut butter, banana and bacon sandwich, she realized he might have been more attracted to the snack than her. She never saw him again and went straight back into Brando’s arms.

Soon after, Moreno discovered she was pregnant with Brando’s child.

“To my shock and horror, Marlon immediately arranged for an abortion,” she says. Brando coldly arranged for a friend to pick up his suffering girlfriend after the illegal procedure.

But the horror continued. Upon her return home, Moreno began bleeding profusely. The abortion was botched — the fetus was dead, but still inside her. She was rushed to the hospital, where the fetus was surgically removed.

Marlon’s response?

He felt he had been “taken” by the abortionist. “Marlon wanted his money back!” she writes.

He then left Moreno to shoot “Mutiny on the Bounty,” where he promptly fell head-over-heels with co-star Tarita Teriipia, whom he would later marry.

When Brando returned home, Moreno had had enough. Left alone in the morning, she scavenged through his medicine cabinet, found his sleeping pills and threw them back in one swallow.

“I went to bed to die. This wasn’t a revenge suicide, but a consolation, an escape-from-pain death,” she writes.

Had Brando’s assistant not checked in on her, she most certainly would have perished. She was rushed to the hospital to have her stomach pumped.

After this final ordeal, her therapist begged her — and Brando — never to see each other again. This time, both agreed.

The suicide attempt occurred shortly after filming wrapped on “West Side Story” — a movie that would earn Moreno an Oscar for Best Supporting Actress and change her life forever.

Although she writes, “Ultimately, I can’t say that anything about the making of ‘West Side Story’ was a mistake, because the movie was brilliant and made history,” she does take shots at the 1961 film.

She writes about her “disdain” for the makeup that was used on the Puerto Rican actors to make all of the Sharks the same color. And she has some unflattering things to say about the female lead, Natalie Wood.

“It was uncomfortable for Hispanics to see Natalie Wood play Maria, especially because we’d heard that Natalie hadn’t wanted the part, but had been so prevailed upon to take it that she couldn’t refuse,” Moreno writes.

She goes on to say that Natalie seemed “uncomfortable” with the group of dancers, who were largely Hispanic.

“This might explain her nonengaging demeanor with us ‘Gypsies’ throughout the shoot. It might have been helpful had we been able to bond with Natalie, but she kept her distance,” Moreno recalls.

After “West Side Story,” Moreno was set up with a Jewish doctor, Lenny Gordon, by a friend. For their first date, Moreno suggested he meet her after a Broadway show.

Gordon was confused, wondering if she was seeing the show alone or, even worse, on another date. He showed up in the lobby, thinking she had stood him up, until he finally looked at the marquee: “Rita Moreno in ‘The Sign in Sidney Brustein’s Window.’ ”

Showing up backstage, he cried, “Wait! You’re the Rita Moreno?”

They married and remained together until his death in 2010.

But Brando loomed as a temptation.

In 1968, looking for work (she was typecast as the plucky Latina after her Oscar win), Moreno reached out to her old paramour. Brando was thrilled; it had been six years since they had been together, and he cast her in his next movie, “The Night of the Following Day,” in which she played his lover.

The film was shot in Brittany, France. And during a reunion dinner and after too many glasses of wine, Moreno fell asleep. She woke up to Brando lying close beside her, his breath on her neck.

“Marlon, we can’t do this. You know we can’t,” she said.

“Just let me sleep with you,” he pleaded. “That’s all I want, to sleep with you.”

She refused.

(It seems Brando was just as obsessed with Moreno as she was with him. In 2005, after his death, some of his possessions were auctioned off. The only piece of movie memorabilia in his Mulholland Drive home was a picture of him in “The Night of the Following Day,” locked in a passionate kiss with a naked Moreno. It hung on the wall of his study.)

One scene in the film required Moreno to slap Brando in the face — and the Method actor wanted it to be hard.

So she did as she was told.

But the smack riled something in him. “I had hit him. Rita Moreno challenged the Marlon Brando. With a you-don’t-do-this-to-me look in his eyes, he hauled off and slammed me with the full force of his powerful arm and open hand,” she writes.

In a moment, all the horror and the mistreatment flooded back to her.

“As the synapses of my brain reconnected, old wounds, hurts, resentment, and disrespect coursed through my body. The festering decay rose like pond scum to the surface, and Rita Moreno emerged as the offended lover,” she writes.

She “went ballistic, insane, crazy” and began to beat him with her fists and shriek like a banshee.

Moreno went home. Unable to watch the dailies, she told Lenny what happened and asked him to see them instead.

“When he returned, he said, ‘Wow, you two were very, very good.’ My sweet husband!”